This application claims the priority of German patent document 198 58 299.4, filed Dec. 17, 1998, the disclosure of which is expressly incorporated by reference herein.
The invention relates to an antenna system for communication between vehicle-mounted navigation systems and satellites for determining the vehicle position, such as the so-called GPS (Global Positioning System).
U.S. Pat. No. 5,105,201 discloses an antenna system for a car radio in which the antenna is arranged on the rear window of a motor vehicle, and a resonant oscillating circuit situated on the exterior side of the rear window is assigned to the antenna. Another resonant oscillating circuit is situated on the interior of the rear window opposite the first resonant oscillating circuit and is electromagnetically coupled with the exterior resonant oscillating circuit and feeds the signals coupled into it to a radio receiver. As the result, the radio receiver can receive radio signals without a direct line connection to the antenna.
In conventional antenna systems of the initially mentioned type, the antenna itself (which, for the purposes of the present application) is frequently constructed as a so-called patch antenna, is provided for the exterior-side mounting on a given mounting surface, for example, on a vehicle rear window. For optimal communication with the satellites situated above the horizon, the selection of a vehicle body part which extends as nearly horizontally as possible is preferred as the mounting surface. The present exterior mounting of the antenna component, in comparison to the alternatively customary systems in which the antenna component is mounted on the inside of the vehicle body, has the advantage that it does not require such precise tuning of the antenna and such an exact mounting of the antenna. It is therefore highly suitable for retrofitting; and in series applications, the need for separate tuning of the antenna to accommodate the material and geometry of the mounting surface for different vehicle types is eliminated.
The antenna systems, for example, for the GPS, usually contain an antenna amplifier (to compensate for line losses and for the impedance matching) which normally forms a common constructional unit with the antenna component and is fed by a direct voltage supply. Furthermore, the antenna system has a signal processing unit, for example, in the form of a receiver and analysis unit; that is, a receiver which demodulates high-frequency locating signals received from the satellite by way of the antenna components, decodes them and determines therefrom the actual vehicle position therefrom, which it then sends as a position data signal with a standardized serial data protocol to a navigation unit.
In addition to the satellite-supported vehicle position determination, conventional antenna systems of the initially mentioned type may also have other functions, for example, for a mobile telephone and/or a car radio, as described in the essays xe2x80x9cDynamic Traffic Control Systemsxe2x80x9d, Funkschau 13/1997, Page 26, and xe2x80x9cMicrostrip Antennasxe2x80x9d, Funkschau 6/1998, Arbeitsblxc3xa4tter Antennen, Part 10, as well as G. Splitt, H. Forster, xe2x80x9cMulti-Element Satellite Mobile Radio Antennas for GPS and Communication Applications in Microstrip Technologyxe2x80x9d, Special Committee xe2x80x9cAntennasxe2x80x9d of the ITG, Discussion Conference of Apr. 1, 1992. These antenna systems and additional antenna systems of this type which are commercially available must penetrate the mounting surface in order to implement the direct-voltage supply line for the antenna amplifier and/or the signal line, by means of which the amplifier output signal is provided to the interior-side signal processing unit. For this purpose, it is known to use a single coaxial cable and by way of this signal cable achieve the power supply as a so-called phantom powering.
German Patent Document DE 43 29 697 A1 describes an access control device (for example, a central locking system of a motor vehicle) which comprises a vehicle-fixed sending and receiving unit. The sending and receiving unit is capable of exchanging information signals with a portable transponder unit in order to permit remote operation of a central locking system outside the vehicle. In a normal operating mode, the transponder unit receives its electric energy from a button cell. In an emergency operating mode, it can draw the energy required for operating the transponder from a prolonged or repeated inquiry code signal which is emitted from the vehicle-fixed sending and receiving unit.
U.S. Pat. No. 5,557,270 discloses a capacitive coupling device for two coaxial cables, which comprises a dielectric plate (for example, a glass plate) with electrodes arranged on opposite sides thereof. The electrodes are each connected by way of an inductance with the line core of the two coaxial cables. On both sides of the dielectric plate, a conductive housing is provided which is connected to the conductive sheath of the coaxial conductors.
One object of the invention is to provide an antenna system of the initially mentioned type which requires no holes in the mounting surface and is largely independent of the material and the geometry of the mounting surface and is therefore well suited also for retrofitting.
This and other objects and advantages are achieved by antenna system according to the invention, which includes a part which is to be arranged on the interior, and a coupling device for coupling an antenna signal and a power supply between the exterior part and the interior part. The coupling devices between the exterior and the interior system parts consist of signal transmission devices which achieve current supply and preferably also the data communication through the mounting surface in a wireless manner, and therefore without requiring breakthroughs or holes in the mounting surface. Current supply preferably takes place inductively.
The antenna system according to the invention is suitable for the mounting on glass and on all other non-conductive mounting surfaces. Because of the exterior arrangement of the antenna component, the difficulties encountered by prior art antennas with respect to damping, disconnecting and tuning of the antenna (inherent, for example, to a behind-the-glass mounting) do not occur. The design of the antenna system remains largely independent of the material and the geometry of the mounting surface and therefore of the vehicle type.
In one embodiment of the invention, the transmission of the data signals received or sent by way of the antenna system (in the following also called antenna signals or useful signals) through the mounting surface takes place capacitively (that is, by means of electric fields), inductively or optically (that is, by means of corresponding electromagnetic waves).
In another embodiment of the antenna system according to the invention, an current is supplied inductively by means of primary and secondary inductive open-field or closed-field helical-path structures which can be implemented in a flat shape and permit the transmission of sufficient energy also, for example, for sending data.
In a further embodiment of the invention, the inductive helical-path structures are implemented in closed-field construction, with a course which at least once changes the looping direction and/or are provided with an encompassing short-circuit mask on their primary and/or secondary side. This permits the transmission of comparatively high energies without an interfering far-field effect. In still a further embodiment of the invention, the short-circuit mask is simultaneously constructed as a heating element, whereby the exterior-side system part can always be maintained at a defined minimum temperature.
In another embodiment, the primary and/or the secondary inductive closed-field structure has on its back side a covering, magnetically conductive field guiding layer, in which the transmitting magnetic field or fields can be guided. The magnetically conductive field guiding layer may be coated in an electrically highly conductive manner on its surface away from the structure so that a magnetic blocking surface is formed, whereby, for example, exterior-side sending and/or receiving components for data signals can be uncoupled with respect to an electromagnetic energy transmission field.
According to a further feature of the invention, an optical transmission of the data signals may take place by means of separate light transmission routes for received data signals and data signals to be sent.
In yet another embodiment of the antenna system according to the invention, an antenna amplifier is assigned to the exterior antenna component. To supply this antenna amplifier with power, corresponding alternating-voltage signals are fed by a coupling coil unit in a wireless manner from the interior through the mounting surface. In addition, a capacitive coupling unit is provided by means of which the amplified antenna signals are transmitted. Further the antenna component, the antenna amplifier and an exterior-side coupling surface of the capacitive coupling unit may be arranged next to or within an exterior-side coupling coil of the coupling coil unit. The last-mentioned variant of a concentric arrangement of the exterior-side system components in the interior of the exterior-side coupling coil minimizes the surface requirement of the antenna construction.
In an antenna system further developed according to the invention, a signal processing unit is assigned to the external antenna component, which signal processing unit comprises a suitable receiving and/or sending part and a pertaining signal processing part, optionally with a signal analyzing function. For their voltage supply, corresponding alternating-voltage signals are guided in a wireless manner from the interior by way of a coupling coil unit through the mounting surface. The coupling coil unit is simultaneously used for the transmission of the antenna signals processed by the signal processing unit.
In a further development of the invention, the antenna component and the signal processing unit are positioned next to or within an exterior coupling coil of the coupling coil unit on the exterior of the mounting surface. The variant with the concentric arrangement of the exterior-side system components in the interior of the exterior-side coupling coil is again particularly suitable for achieving a minimum surface requirement.
In still another embodiment of the invention, an antenna amplifier and/or a signal processing unit is provided in the interior of the vehicle, and not on the exterior side of the vehicle. The antenna signals (the signals supplied by or fed to the antenna component) are transmitted by a capacitive coupling unit in a wireless manner through the mounting surface between the antenna component and the amplifier or the signal processing unit.
Finally, according to another feature of the invention, the interior-side system part contains a coaxial line which carries the antenna signals as well as the power supply alternating-voltage signals. For this purpose, the two signal types are situated in preferably considerably different frequency ranges.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.